Organic photoelectric conversion element, image pickup element, and image pickup apparatus

ABSTRACT

The present disclosure provides an organic compound represented by general formula [1] below. 
     
       
         
         
             
             
         
       
     
     In formula [1], Ar 1  and Ar 2  each represent an alkyl group having 1 to 8 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or a heteroaromatic group having 3 to 17 carbon atoms. Ar 1  and Ar 2  may be the same or different. Ar 3  and Ar 4  are each a substituent having a carbazolyl group. Ar 3  and Ar 4  may be the same or different. Ar 1  to Ar 4  may be substituted. At least one of Ar 1  to Ar 4  has a tert-butyl group. The total number of tert-butyl groups in one molecule of the organic compound is 2 or more.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. App. No. 16/714,290, filedDec. 13, 2019, which is a Continuation of International PatentApplication No. PCT/JP2018/023152, filed Jun. 18, 2018, which claims thebenefit of Japanese Patent Application No. 2017-123089, filed Jun. 23,2017, each of which is hereby incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present invention relates to an organic photoelectric conversionelement, an image pickup element including the organic photoelectricconversion element, and an image pickup apparatus including the organicphotoelectric conversion element.

BACKGROUND ART

Planar light-receiving elements are widely used as image pickup elementsin cameras and the like. Such a planar light-receiving element includesa two-dimensional array of pixels having photodiodes. Upon receivinglight, the planar light-receiving element generates a signal. The signalis read out, and a CCD circuit or a CMOS circuit performs imageprocessing. In the related art, silicon and other semiconductorsubstrates having photoelectric conversion units formed therein are usedas the above image pickup elements.

Elements including photoelectric conversion units made of organiccompounds, that is, organic photoelectric conversion elements are underdevelopment. It is expected that high absorption coefficients andflexibility of organic compounds enable image pickup elements havingimproved properties such as higher sensitivity, slimmer profiles,lighter weights, and higher flexibility.

In such image pickup elements, dark current is known to causedegradation of the quality of captured images. Various studies have beenconducted to reduce dark current in organic photoelectric conversionelements.

PTL 1 discloses that after an element is fabricated, heat treatment(annealing) at high temperature is performed to reduce dark current.

PTL 2 discloses that a compound represented by the following structuralformula (hereinafter referred to, for example, as compound 1-A) is usedin an organic light-emitting element.

To reduce dark current, it is preferable to perform sublimationpurification of an organic compound used in an organic photoelectricconversion element or to perform an annealing step after the organicphotoelectric conversion element is fabricated. However,high-temperature annealing of an organic compound layer may cause theorganic compound to undergo crystallization, which can lead todegradation of element properties. As well as preferred examples, PTL 1also discloses that after annealing, dark current is increased ratherthan decreased to reduce external quantum efficiency.

Compound 1-A disclosed in PTL 2 does not have a sufficiently high glasstransition temperature, and thus may undergo crystallization in ahigh-temperature annealing step, leading to degradation of elementproperties.

The present invention has been made to overcome the above disadvantages,and an object thereof is to provide an organic compound having highsublimability and a high glass transition temperature.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Laid-Open No. 2011-187937-   PTL 2: Korean Patent Laid-Open No. 2015-0086994

SUMMARY OF INVENTION

Thus, the present invention provides an organic compound represented bygeneral formula [1] below.

In formula [1], Ar₁ and Ar₂ represent an alkyl group having 1 to 8carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms,or a heteroaromatic group having 3 to 17 carbon atoms. Ar₁ and Ar₂ maybe the same or different. Ar₃ and Ar₄ are selected from the groupconsisting of substituents represented by general formulae [2a] to [2c].Ar₃ and Ar₄ may be the same or different.

Ar₁ to Ar₄ are each optionally substituted with a substituent selectedfrom the group consisting of a halogen atom, a cyano group, an alkylgroup having 1 to 8 carbon atoms, and an alkoxy group having 1 to 8carbon atoms. The alkyl group is optionally substituted with a fluorineatom. At least one of Ar₁ to Ar₄ has a tert-butyl group. The totalnumber of tert-butyl groups in one molecule of the organic compound is 2or more.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates a molecular structure of exemplarycompound A2 and a molecular structure of comparative compound 1.

FIG. 2 is a graph of an absorption spectrum of exemplary compound A2 ina solution and an absorption spectrum of a thin film formed from thesolution.

FIG. 3 is a schematic view of an example of an organic photoelectricconversion element according to an embodiment.

FIG. 4 is a schematic diagram illustrating an example of a pixel circuitincluding an organic photoelectric conversion element according to anembodiment.

FIG. 5 is a schematic diagram illustrating an example of a peripheralcircuit including an organic photoelectric conversion element accordingto an embodiment.

DESCRIPTION OF EMBODIMENTS

The present invention is an organic compound represented by generalformula [1] below.

In formula [1], Ar₁ and Ar₂ each represent an aromatic hydrocarbon grouphaving 6 to 18 carbon atoms or a heteroaromatic group having 3 to 17carbon atoms. Ar₃ and Ar₄ are selected from the group consisting ofsubstituents represented by general formulae [2a] to [2c] below. Atleast one of Ar₁ to Ar₄ has a tert-butyl group.

Examples of aromatic hydrocarbon groups represented by Ar₁ and Ar₂include phenyl, naphthyl, phenanthryl, fluorenyl, chrysenyl,triphenylenyl, and pyrenyl. From the viewpoint of sublimability,substituents having relatively small molecular weights are preferred.Specifically, phenyl and naphthyl are preferred.

Examples of heteroaromatic groups represented by Ar₁ and Ar₂ includepyridyl, pyrazinyl, pyrimidinyl, quinolyl, isoquinolyl, thienyl,furanyl, benzothienyl, benzofuranyl, and triazinyl. From the viewpointof sublimability and stability, substituents having relatively smallmolecular weights and high stability are preferred. Specifically,pyridyl, benzothienyl, and benzofuranyl are preferred.

Ar₃ and Ar₄ are substituents selected from the group consisting ofsubstituents represented by general formulae [2a] to [2c]. Of thesubstituents represented by formulae [2a] to [2c], the substituentrepresented by formula [2a], which has a relatively small molecularweight, is preferred in view of sublimability.

Ar₁ to Ar₄ may be substituted with a halogen atom, for example,fluorine, chlorine, bromine, or iodine, preferably, fluorine.

Ar₁ to Ar₄ may be substituted with a cyano group.

Ar₁ to Ar₄ may be substituted with an alkyl group, for example, an alkylgroup having 1 to 8 carbon atoms. Specific examples include methyl,ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl,n-pentyl, n-hexyl, cyclohexyl, n-heptyl, and n-octyl. Methyl andtert-butyl are preferred. The alkyl group may be substituted with afluorine atom. The alkyl group substituted with a fluorine atom ispreferably a trifluoromethyl group.

Ar₁ to Ar₄ may be substituted with an alkoxy group, for example, analkoxy group having 1 to 8 carbon atoms. Specific examples includemethoxy, ethoxy, propoxy, butoxy, pentoxy, and hexoxy. Methoxy ispreferred.

At least one of Ar₁ to Ar₄ has a tert-butyl group, and the total numberof tert-butyl groups contained in Ar₁ to Ar₄ is 2 or more. Preferably,the total number of tert-butyl groups contained in Ar₁ to Ar₄ is 4 ormore.

The total number of tert-butyl groups contained in Ar₁ to Ar₄ is 2 ormore. This is because the electron blocking ability and thermalstability of the organic compound cannot sufficiently be improved whenthe number of tert-butyl groups is 1.

The total number of tert-butyl groups contained in Ar₁ to Ar₄ ispreferably 4 or more, more preferably 6 or more. In view of holetransportability, the number of tert-butyl groups is preferably 10 orless. That is, the number of tert-butyl groups in one molecule of theorganic compound according to the present invention may be 2 to 10, 4 to10, or 6 to 10.

The organic compound according to the present invention has a high glasstransition temperature and a low LUMO level and thus can be used, forexample, for an electron blocking layer of an organic electronicelement. The electron blocking layer is a layer less likely to receiveelectrons. LUMO means the lowest unoccupied molecular orbital. Having alow LUMO level means having a LUMO level closer to the vacuum level. Alow LUMO level is also expressed as a shallow LUMO level. The same canbe said for a HOMO (highest occupied molecular orbital) level.

Characteristics of Organic Compound According To Present Invention

The organic compound according to the present invention has a benzenering substituted with Ar₁ to Ar₄, as represented by general formula [1].Ar₃ and Ar₄ each have a carbazolyl group, as shown in general formulae[2a] to [2c]. At least one of Ar₁ to Ar₄ has a tert-butyl group, and thetotal number of tert-butyl groups contained in Ar₁ to Ar₄ is 2 or more.With this configuration, the compound of general formula [1] has thefollowing characteristics (1) to (6).

-   (1) Being readily formed into an amorphous thin film-   (2) Having a wide band gap and low absorption in the visible light    range-   (3) Having high hole transportability-   (4) Having high electron blocking ability-   (5) Having high thermal stability-   (6) Having high sublimability

These characteristics will be described below.

Being Readily Formed into an Amorphous Thin Film

The organic compound according to the present invention has a benzenering substituted with Ar₁ to Ar₄, as represented by general formula [1].With this configuration, repulsion due to steric hindrance occurs tocause the whole molecule to have a twisted structure. Here, themolecular structure of exemplary compound A2 according to the presentinvention and comparative compound 1 in FIG. 1 , which is a compoundhaving a structure represented by general formula [1] where Ar₁ and Ar₂are each a hydrogen atom and Ar₃ and Ar₄ are each represented by formula[2a], was estimated by molecular orbital calculation. The planarity ofthe estimated molecular skeletons was evaluated by comparing theirdihedral angles. The dihedral angles compared were dihedral anglesbetween the benzene ring in general formula [1] and its adjacent benzenering. FIG. 1 illustrates molecular structures of exemplary compound A2and comparative compound 1 as observed in the horizontal direction andthe vertical direction. The dihedral angle of comparative compound 1 was36.0°, whereas the dihedral angle of exemplary compound A2 according tothe present invention was 47.4°. Exemplary compound A2 was found to havea highly twisted structure.

An organic compound having such a twisted structure is less likely toundergo molecular packing. Molecular packing is a phenomenon wheremolecules are stacked on top of each other by intermolecularinteraction. Aromatic compounds have highly planar molecular skeletonsand strong intermolecular interactions and thus are likely to undergoaccelerated molecular packing. Compounds having a carbazolyl group arealso likely to undergo molecular packing because the carbazolyl groupitself has high planarity. Molecular packing is unfavorable because itcan cause crystallization.

Molecular packing can be reduced, for example, by incorporating manysubstituents, but this method involves an increase in molecular weightand thus is not preferred from the viewpoint of sublimability. Theorganic compound according to the present invention, whose basicmolecular skeleton itself is twisted and which has a nonplanar molecularstructure, is less likely to undergo molecular packing. Therefore, theorganic compound according to the present invention is readily formedinto an amorphous thin film.

To achieve high external quantum efficiency and low dark current in anorganic photoelectric conversion element, it is preferable to use acompound formable into an amorphous film. This is because a film havinga grain boundary traps carriers to cause a decrease in photoelectricconversion efficiency and an increase in dark current. The same can besaid for an electron blocking layer and a hole blocking layer disposedbetween a photoelectric conversion layer and an electrode.

In particular, an organic compound layer in contact with an electrode ispreferably an amorphous thin film. This is because a film in anaggregated state induced by crystallization is ununiform, andaccordingly the electric field may be locally concentrated in the film.Such a local electric field concentration can cause a leakage current oran in-plane variation in sensitivity, thus reducing the stability ofelement properties.

Thus, the organic compound according to the present invention is readilyformed into an amorphous thin film and hence is suitable for use as aconstituent material of an organic photoelectric conversion element.

The molecular orbital calculation was performed by the densityfunctional theory (DFT), which is now widely used. The B3LYP functionaland the 6-31G* basis function were used. The molecular orbitalcalculation was performed by Gaussian 09 (Gaussian 09, Revision C.01, M.J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H.Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J.Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R.Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H.Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M.Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T.Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C.Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M.Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski,G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox,Gaussian, Inc., Wallingford CT, 2010), which is now widely used.

Having a Wide Band Gap and Low Absorption in the Visible Light Range

As described above, the organic compound according to the presentinvention has a benzene ring substituted with Ar₁ to Ar₄, as representedby general formula [1], and thus the whole molecule has a twistedstructure. Due to this structure, the conjugation of molecules isbroken, and thus the compound has a wide band gap. That is, the compoundhas a wide band gap and low absorption in the visible light range. Thewide band gap is also due to the reduced molecular packing described in(1). It is known that an organic compound, when formed into a thin film,experiences a phenomenon in which the apparent conjugation length isincreased by molecular packing and the absorption wavelength becomeslonger, that is, the band gap becomes narrower. The compound of generalformula [1] according to the present invention has a structure that cansufficiently reduce molecular packing and thus is less likely to have anarrower band gap when formed into a thin film.

In an organic photoelectric conversion element, a larger amount of lightpreferably reaches a photoelectric conversion layer. For example, in thecase of a structure in which an electron blocking layer or the like isdisposed on the light incident side of the photoelectric conversionlayer, when the electron blocking layer has absorption in the visiblerange, the amount of light reaching the photoelectric conversion layeris small, leading to low external quantum efficiency. Therefore, theelectron blocking layer is preferably formed of a compound having lowabsorption in the visible range.

On the other hand, the electron blocking layer preferably has a largethickness to sufficiently suppress electron injection from an electrode.If the thickness is not sufficiently large, tunnel electron injectionmay occur when a voltage is applied, or irregularities and foreignmatter on the electrode surface cannot sufficiently be covered, whichmay cause a physical short circuit or a leakage current.

When the thickness is not sufficiently large, the layer is less likelyto have a uniform thickness. In this case, the photoelectric conversionlayer and the electrode are locally adjacent to each other, and thus theelectric field may be concentrated in the adjacent area to cause chargeinjection from the electrode.

Therefore, the electron blocking layer is preferably formed of acompound that, when formed into a layer with a sufficiently largethickness, has low absorption in the visible light range so as not toreduce the amount of light reaching the photoelectric conversion layer.

FIG. 2 is a graph of absorption spectra of a diluted toluene solution(dotted line) of exemplary compound A2 according to the presentinvention and its deposited film (solid line). The optical band gaps ofexemplary compound A2 were calculated from absorption edges in theabsorption spectra; the band gap estimated from the toluene solution was3.42 eV, and the band gap estimated from the deposited film was 3.36 eV.The results show that the band gap slightly becomes narrower by 0.06 eVafter the thin film formation.

The fact that the band gap after the thin film formation is 3.36 eV (369nm, in terms of wavelength) indicates that exemplary compound A2 hassufficiently low absorption in the visible light range (blue: 450 nm tored: 620 nm) when formed into a thin film.

Thus, the compound according to the present invention represented bygeneral formula [1] has a wide band gap and low absorption in thevisible light range when formed into a thin film and thus is suitablefor use as a constituent material of an organic photoelectric conversionelement. In particular, the compound is preferably used as a layer incontact with an electrode.

The absorption spectra were measured using a V-560 manufactured by JASCOCorporation as a measuring device. The solution sample was measuredusing a quartz cell, and the deposited film sample used for themeasurement was formed by deposition on a quartz substrate at a degreeof vacuum of 5 × 10⁻⁴ Pa or less.

Having High Hole Transportability

To achieve high external quantum efficiency in an organic photoelectricconversion element, charges generated in a photoelectric conversionlayer are preferably transported rapidly to an electrode. For example,holes generated in the photoelectric conversion layer reach a cathodeafter passing through, for example, an electron blocking layer. Asdescribed above, the electron blocking layer preferably has asufficiently large thickness to sufficiently suppress electron injectionfrom the electrode.

That is, the electron blocking layer, while having a sufficiently largethickness, is preferably able to transport holes generated in thephotoelectric conversion layer rapidly to the cathode.

The organic compound according to the present invention has a benzenering substituted with Ar₃ and Ar₄, as represented by general formula[1]. Ar₃ and Ar₄ each have a carbazolyl group. That is, the organiccompound according to the present invention has a molecular structurewhose both ends are terminated with a carbazolyl group, which has highhole transportability, and thus has high hole transportability. Thus,the organic compound according to the present invention can be suitablyused for an electron blocking layer of an organic photoelectricconversion element.

Having High Electron Blocking Ability

To suppress charge injection from an electrode and reduce dark currentin an organic photoelectric conversion element, the injection barrierbetween the electrode and a charge blocking layer is preferablysufficiently large. For example, an electron blocking layer disposedbetween a photoelectric conversion layer and a cathode preferably has alow LUMO level to sufficiently suppress injection of electrons from thecathode.

The organic compound according to the present invention has a wide bandgap, as described in (2). The organic compound according to the presentinvention has a low HOMO level because of having, in its molecularstructure, two or more tert-butyl groups, which are alkyl groups havingelectron-donating properties. Therefore, the organic compound accordingto the present invention has a wide band gap and a low HOMO level.Consequently, the compound has a low LUMO level.

The LUMO level of the organic compound formed into a thin film can becalculated by subtracting an energy corresponding to an optical band gapcalculated from an absorption spectrum from a HOMO level determined froman ionization potential.

A deposited film of exemplary compound A2 according to the presentinvention was formed by deposition on an AlN substrate at a degree ofvacuum of 5 × 10⁻⁴ Pa or less. The ionization potential of the film wasmeasured using an AC-3 manufactured by Riken Keiki Co., Ltd. to be 6.09eV.

As described above, the optical band gap was 3.36 eV, and thus the LUMOlevel can be estimated to be 2.73 eV, indicating that the filmsufficiently functions as an electron blocking layer. Comparativecompound 2 (compound 1-A disclosed in PTL 2) was subjected to the samemeasurement, and its LUMO level was calculated to be 2.93 eV. Thesevalues show that comparative compound 2 has lower electron blockingability than exemplary compound A2 according to the present invention.

Thus, the organic compound according to the present invention has highelectron blocking ability and can be suitably used for an electronblocking layer of an organic photoelectric conversion element.

Having High Thermal Stability

In an organic photoelectric conversion element, thermal stability isrequired under high-temperature conditions during a process for forminga color filter and a process for mounting a photosensor, for example, awire bonding process. Being thermally stable means not being thermallydecomposed and staying amorphous under high-temperature conditions. Tostay amorphous, it is preferable to have a high glass transitiontemperature. The glass transition temperature of an organic compounddepends greatly on its molecular weight. Thus, one possible way todesign an organic compound having a high glass transition temperaturesufficient to withstand high-temperature processes is to increase themolecular weight of the organic compound.

However, increasing the molecular weight reduces sublimability, asdescribed below. Thus, not all substituents may be incorporated, and itis preferable to select an appropriate substituent. The organic compoundaccording to the present invention has at least two tert-butyl groupsand thus has a high glass transition temperature and high sublimability.

The glass transition temperatures of exemplary compound A2 according tothe present invention and comparative compound 2 were evaluated bydifferential scanning calorimetry (DSC). In the DSC, a sample of about 2mg was placed in an aluminum pan, and the pan is then sealed and rapidlycooled from a high temperature over the melting point to bring thesample into an amorphous state, after which the temperature was raisedat a rate of 10° C./min, thereby determining the glass transitiontemperature. A Pyris1 DSC manufactured by PerkinElmer Inc. was used as ameasuring device.

The measurement revealed that exemplary compound A2 had a glasstransition temperature of 200° C. and comparative compound 2 had a glasstransition temperature of 160° C. The glass transition temperatures ofthe compounds are shown in Table 1 together with their decompositiontemperatures and sublimation temperatures.

Thus, the organic compound according to the present invention has highthermal stability and can sufficiently withstand the process formounting a photosensor. Using this compound can provide a stable organicphotoelectric conversion element that can maintain its elementproperties after being subjected to a high-temperature process.

Having High Sublimability

In an organic photoelectric conversion element, the purity of theorganic compound is preferably increased by sublimation purification.This is because if the organic compound contains impurities, traps andfree carriers derived from the impurities cause, for example, a localleakage current, leading to an increase in dark current.

The organic compound according to the present invention has highsublimability. This will be described. A compound obtained by replacingtert-butyl groups of exemplary compound A2 according to the presentinvention with phenyl groups is used as comparative compound 3.Comparative compound 3 has a molecular weight of 1017.26 and thus can beconsidered to have a high glass transition temperature and high thermalstability.

Exemplary compound A2 according to the present invention, comparativecompound 2, and comparative compound 3 were each subjected tosublimation purification.

In the operation of sublimation purification, the temperature wasgradually raised at a degree of vacuum of 1 × 10⁻¹ Pa under a flow of Arto initiate sublimation purification. The sublimation temperature is atemperature at which a sufficient sublimation rate is reached.

Exemplary compound A2 sublimed at 410° C. That is, the sublimationtemperature of A2 is 410° C. In the case of comparative compound 3, apartial sublimate was yielded at 470° C., but a decrease in purity dueto thermal decomposition occurred, resulting in unsuccessful sublimationpurification. This is probably because the sublimation temperature andthe thermal decomposition temperature of comparative compound 3 areclose to each other.

Thus, exemplary compound A2 according to the present invention andcomparative compounds 2 and 3 were subjected to TG/DTA measurement. Thedecomposition temperature is a temperature at which the weight lossreaches 5%. Exemplary compound A2 according to the present invention hada decomposition temperature of 480° C. Comparative compounds 2 and 3 hada decomposition temperature of 480° C.

Exemplary compound A2 has a temperature difference between sublimationtemperature and decomposition temperature of 70° C., whereas comparativecompound 3 has a temperature difference of 10° C. The temperaturedifference of comparative compound 3 is small. That is, comparativecompound 3, whose sublimation temperature and thermal decompositiontemperature are close to each other, is a material unsuitable as aconstituent material of an organic photoelectric conversion element.

Therefore, the organic compound according to the present invention has alarge difference between sublimation temperature and thermaldecomposition temperature because of having 2 or more tert-butyl groups,and the purity of the compound can be increased by sublimationpurification.

TABLE 1 Structure Glass transition temperature SublimabilityDecomposition temperature -sublimation temperature Evaluation Exemplarycompound A2

200° C. 480° C. - 410° C. Sublimable Comparative compound 2

160° C. 480° C. - 380° C. Sublimable Comparative compound 3

200° C. 480° C. - 470° C. Unsublimable

Therefore, the organic compound according to the present invention hasthe above characteristics (1) to (6) and thus has higher sublimabilityand a higher glass transition temperature than comparative compounds 1to 3. The organic compound according to the present invention can besuitably used for an organic photoelectric conversion element. Inparticular, the compound of general formula [1] can be suitably used foran electron blocking layer.

When the compound of general formula [1] is used for an organic layer ofan organic photoelectric conversion element, the layer containing thecompound of general formula [1] may be formed, for example, by a spincoating method, but preferably by deposition under vacuum (a vacuumdeposition method). This is because the vacuum deposition method canform a high-purity thin film. When the vacuum deposition method is used,the required temperature typically increases as the molecular weight ofthe organic compound used as a constituent material of the layerincreases. When the required temperature reaches an excessively highdecomposition temperature, the organic compound used as a constituentmaterial is likely to undergo thermal decomposition.

Examples of Organic Compounds According to Present Invention

Specific examples of the compound of general formula [1] are shownbelow. It should be noted that, in the present invention, the compoundof general formula [1] is not limited to these specific examples.

Of the exemplary compounds, exemplary compounds of group A have astructure in which Ar₁ and Ar₂ in formula [1] are each a substituted orunsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms.Exemplary compounds of group A have high thermal stability and highsublimability because Ar₁ and Ar₂ are each an aromatic hydrocarbongroup.

Exemplary compounds A1 to A12 have particularly high thermal stabilityand high sublimability because Ar₁ and Ar₂ in formula [1] are each aphenyl group and Ar₃ and Ar₄ in formula [1] are each a substituentrepresented by general formula [2a].

Exemplary compounds A13 to A16 have high thermal stability because Ar₃and Ar₄ in formula [1] are each a substituent represented by generalformula [2b] or [2c].

Furthermore, exemplary compounds A25 to A28 have various alkyl groups,particularly, a linear alkyl group (e.g., n-butyl) or a cycloalkyl group(e.g., cyclohexyl), and thus have high solubility. In other words, thesecompounds have a linear or cyclic alkyl group having 4 or more carbonatoms. Thus, these compounds are suitable for use in forming a film bycoating.

Exemplary compounds of group B have a structure in which at least one ofAr₁ to Ar₄ in formula [1] is bonded to a meta position of a benzeneskeleton or a peri position of a naphthalene skeleton. Thus, the wholemolecular structure of these compounds is greatly twisted. That is,exemplary compounds of group B are particularly advantageous in thattheir molecular structure has many twisted portions due to thesubstitution position and thus a highly amorphous organic compound layeris formed. The benzene skeleton is a concept including a benzene ringconstituting a carbazolyl group. Exemplary compound B12, which has abond at the 3-position of a carbazolyl group, is a compound in which thebenzene ring in general formula [1] is bonded at a meta position of abenzene skeleton.

Exemplary compounds of group C have a structure in which at least one ofAr₁ and Ar₂ in formula [1] is a substituted or unsubstitutedheteroaromatic group having 3 to 17 carbon atoms. When theheteroaromatic ring has a nitrogen atom, the compound itself has a high(or, a deep) oxidation potential because of the electron-withdrawingpower of the nitrogen atom and thus is resistant to oxidation.

When the heteroaromatic ring has a sulfur atom or an oxygen atom, thecompound has a strong intermolecular interaction because the sulfur atomand the oxygen atom have many unshared electron pairs, and thus thecompound has high carrier transportability.

That is, exemplary compounds of group C are particularly advantageous inthat the compounds have stability and carrier transportability due tothe electronic effects. These compounds can also be used for a holeblocking layer.

Of the exemplary compounds, A1 to A20, A26 to A31, B1 to B12, and C3 toC18 are excellent in the above-described characteristics (1), (2), and(4) to (6) because the total number of tert-butyl groups is 4 or more.Thus, these compounds are suitable as a material for an organicphotoelectric conversion element.

Of the exemplary compounds, A2 to A6, A10 to A12, A15 to A17, B1 to B5,and C7 to C9 are more excellent in the above-described characteristicsbecause the total number of tert-butyl groups is 6 or more. Thus, thesecompounds are suitable for use.

Photoelectric Conversion Element According To Embodiment PhotoelectricConversion Element

FIG. 3 is a schematic sectional view of an example of a photoelectricconversion element according to an exemplary embodiment. Thephotoelectric conversion element includes an anode 5, a cathode 4, and afirst organic compound layer 1 disposed therebetween. The first organiccompound layer 1 forms a photoelectric conversion unit that convertslight into charges. Hence, the first organic compound layer can also becalled a photoelectric conversion layer.

When the photoelectric conversion element includes a plurality oflayers, the plurality of layers are preferably stacked from the anodetoward the cathode.

The photoelectric conversion element may further include a secondorganic compound layer 2 disposed between the first organic compoundlayer 1 and the cathode 4 and a third organic compound layer 3 disposedbetween the first organic compound layer 1 and the anode 5.

A protective layer 7 is disposed on the cathode. A wavelength selectionunit 8 is disposed on the protective layer 7. A microlens 9 is disposedon the wavelength selection unit 8. A readout circuit 6 is connected tothe anode. The photoelectric conversion element may be disposed on asubstrate (not illustrated).

In the photoelectric conversion element, a voltage may be appliedbetween the anode and the cathode when photoelectric conversion isperformed. The voltage depends on the total thickness of the organiccompound layers but is preferably about 1 V or more and 15 V or less,more preferably about 2 V or more and 10 V or less.

Substrate

The organic photoelectric conversion element according to the presentembodiment may include a substrate. Examples of substrates include glasssubstrates, flexible substrates, and semiconductor substrates.

The photoelectric conversion element according to the present embodimentmay include a semiconductor substrate. The constituent elements of thesemiconductor substrate are not limited as long as a charge accumulationunit and a floating diffusion (FD) can be formed by impurityimplantation. Examples of such constituent elements include Si, GaAs,and GaP. In particular, Si is preferred.

The semiconductor substrate may be an N-type epitaxial layer. In thiscase, a P-type well, an N-type well, a P-type semiconductor region, andan N-type semiconductor region are formed in the semiconductorsubstrate.

The charge accumulation unit is an N-type or a P-type semiconductorregion that is formed in the semiconductor substrate by ion implantationand that accumulates charges generated from the photoelectric conversionunit.

When electrons are accumulated, an N-type semiconductor region may beformed in a surface of the semiconductor substrate, or an accumulationdiode having a P-N structure may be formed from the surface of thesubstrate. In both cases, electrons can be accumulated in the N-typesemiconductor region.

When holes are accumulated, a P-type semiconductor region may be formedin the semiconductor substrate, or an accumulation diode having an N-Pstructure may be formed from the surface of the substrate. In bothcases, holes can be accumulated in the P-type semiconductor region.

The accumulated charges are transferred from the charge accumulationunit to the FD. The charge transfer may be controlled by a gateelectrode. The charges generated from the organic compound layers areaccumulated in the charge accumulation unit, and the charges accumulatedin the charge accumulation unit are transferred to the FD. The chargesare then converted into current by an amplifier transistor, which willbe described later.

When the charge accumulation unit has a P-N junction formed therein,photoelectric conversion may be performed with light leaking from thephotoelectric conversion unit.

A charge output unit may be formed instead of the charge accumulationunit. When an output unit is formed, charges are transferred from theelectrode to the amplifier transistor and others not via the FD.

Anode

The anode is an electrode that collects electrons of charges generatedfrom the photoelectric conversion layer. In an image pickup element, theanode may be a pixel electrode. The anode may be disposed closer to apixel circuit than the cathode is to the pixel circuit. The anode,because of its function, can also be called an electron collectingelectrode.

Examples of constituent materials of the anode include ITO, indium zincoxide, SnO₂, antimony-doped tin oxide (ATO), ZnO, Al-doped zinc oxide(AZO), gallium-doped zinc oxide (GZO), TiO₂, and fluorine-doped tinoxide (FTO).

Cathode

The cathode is an electrode that collects holes of charges generatedfrom the photoelectric conversion layer. In an image pickup element, thecathode may be a pixel electrode.

Specific examples of constituent materials of the cathode includemetals, metal oxides, metal nitrides, metal borides, organic conductivecompounds, and mixtures thereof. More specific examples includeconductive metal oxides such as antimony-doped tin oxide (ATO),fluorine-doped tin oxide (FTO), tin oxide, zinc oxide, indium oxide,indium tin oxide (ITO), and indium zinc oxide; metal materials such asgold, silver, magnesium, chromium, nickel, titanium, tungsten, andaluminum; conductive compounds such as oxides and nitrides of thesemetal materials (e.g., titanium nitride (TiN)); mixtures and laminatesof these metals and conductive metal oxides; inorganic conductivematerials such as copper iodide and copper sulfide; organic conductivematerials such as polyaniline, polythiophene, and polypyrrole; andlaminates of these materials and ITO or titanium nitride. Particularlypreferably, the constituent material of the cathode is a materialselected from a magnesium-silver alloy, titanium nitride, molybdenumnitride, tantalum nitride, and tungsten nitride.

The pixel electrode may be an anode or a cathode. The electrode on thelight-emission side preferably has high transparency, specifically, 80%or more.

The electrode on the light incident side can also be called the upperelectrode. In this case, the other is called the lower electrode.

The above-described two electrodes (the anode and the cathode) can eachbe formed by a method appropriately selected in consideration ofsuitableness for electrode materials used. Specifically, for example,wet methods such as printing methods and coating methods; physicalmethods such as vacuum deposition methods, sputtering methods, and ionplating methods; and chemical methods such as CVD and plasma CVD methodscan be used.

When ITO is used to form the electrodes, the electrodes can be formed,for example, by an electron beam method, a sputtering method, aresistance heating deposition method, a chemical reaction method (e.g.,a sol-gel method), or application of a dispersion of indium tin oxide.

In this case, the surfaces of the electrodes (ITO electrodes) formed maybe subjected to UV-ozone treatment, plasma treatment, or othertreatment.

When TiN is used to form the electrodes, various film-forming methodsincluding reactive sputtering methods can be used. In this case, theelectrodes (TiN electrodes) formed may be subjected to annealingtreatment, UV-ozone treatment, plasma treatment, or other treatment.

First Organic Compound Layer

The first organic compound layer can also be called a photoelectricconversion layer, as described above. Constituent materials of thephotoelectric conversion layer of the organic photoelectric conversionelement according to the present embodiment will be described. Thephotoelectric conversion layer preferably has high light absorptivityand efficiently effects charge separation of received light, that is,preferably offers high photoelectric conversion efficiency.

The photoelectric conversion layer is preferably able to transportgenerated charges, that is, electrons and holes, rapidly to theelectrodes. To prevent degradation of film quality, such ascrystallization, the photoelectric conversion layer is preferably madeof a material having a high glass transition temperature. For higherfilm quality, the photoelectric conversion layer may be a layer of amixture with a material having a high glass transition temperature.

The first organic compound layer may contain a plurality of organiccompounds. When the first organic compound layer contains a plurality oforganic compounds, a mixture of the plurality of organic compounds maybe contained in a single layer, or the plurality of organic compoundsmay be contained in a plurality of layers.

The first organic compound layer preferably contains a p-type organicsemiconductor or an n-type organic semiconductor, more preferablycontains, as at least a part thereof, a bulk heterojunction layer (mixedlayer) in which an organic p-type compound and an organic n-typecompound are mixed together.

The presence of the bulk heterojunction layer in the first organiccompound layer can provide improved photoelectric conversion efficiency(sensitivity). The presence of the bulk heterojunction layer in anoptimum proportion can increase the electron mobility and the holemobility of the first organic compound layer 1 to increase thephotoresponse speed of the photoelectric conversion element.

The first organic compound layer preferably contains, as the n-typeorganic semiconductor, fullerene or a fullerene analogue. Electron pathsare formed by fullerene molecules or fullerene analogue molecules, thusimproving electron transportability to improve the responsiveness of thephotoelectric conversion element.

The fullerene content or the fullerene analogue content is preferably 20vol% or more and 80 vol% or less, provided that the total volume of thephotoelectric conversion layer is 100 vol%.

The term “fullerene analogue” is the generic name of closed-shell hollowclusters consisting only of many carbon atoms. Examples thereof includeC60 and higher-order fullerenes such as C70, C74, C76, and C78. Thesematerials may be used alone or in combination. As a material used forcharge separation and electron transport, other different materials maybe used together with the fullerene analogues. Examples of materialsother than fullerene include naphthalene compounds such as NTCDI,perylene compounds such as PTCDI, phthalocyanine compounds such asSubPc, and thiophene compounds such as DCV3T, which are known as n-typeorganic semiconductors.

Examples of fullerene analogues include fullerene C60, fullerene C70,fullerene C76, fullerene C78, fullerene C80, fullerene C82, fullereneC84, fullerene C90, fullerene C96, fullerene C240, fullerene 540, mixedfullerene, and fullerene nanotubes.

Examples of p-type organic semiconductors contained in the photoelectricconversion element include the following organic compounds. The organiccompounds represented by the following structural formulae may besubstituted, for example, with an alkyl group as long as their functionis not adversely affected.

Second Organic Compound Layer

The second organic compound layer inhibits electrons from entering thefirst organic compound layer from the cathode and preferably has a lowelectron affinity (close to the vacuum level). A low electron affinitycan translate into a low LUMO level. The second organic compound layer,because of its function, can also be called an electron blocking layer.The second organic compound layer 2 may be formed of multiple layers ora bulk heterojunction layer (mixed layer).

The electron blocking layer preferably contains the organic compoundaccording to the present invention. Other functional layers may bedisposed between the cathode and the electron blocking layer.

Third Organic Compound Layer

The third organic compound layer inhibits holes from entering the firstorganic compound layer from the anode and preferably has a highionization potential (distant from the vacuum level). A high ionizationpotential can translate into a high HOMO level. The third organiccompound layer, because of its function, can also be called a holeblocking layer. The third organic compound layer 3 may be formed ofmultiple layers or a bulk heterojunction layer (mixed layer). Otherfunctional layers may be disposed between the anode and the holeblocking layer.

Protective Layer

The protective layer 7 is formed on the upper portion of the electrodeand is preferably an insulating layer. The protective layer may beformed of a single material or a plurality of materials. When formed ofa plurality of materials, the protective layer may be a stack of theplurality of layers or a layer in which the plurality of materials aremixed together. Examples of constituent materials of the protectivelayer include organic materials such as resins, and inorganic materialssuch as silicon nitride, silicon oxide, and aluminum oxide. Theprotective layer can be formed by sputtering, atomic layer deposition(ALD), or other methods. Silicon nitride is also expressed as SiNx, andsilicon oxide as SiOx. X is a numerical value representing an elementalratio.

A planarizing layer may be disposed on the protective layer 7. Theplanarizing layer is disposed in order to eliminate the effect of thesurface state of the protective layer on the wavelength selection unit.The planarizing layer can be formed by a known production method such asa coating method or a vacuum deposition method. For example,chemical-mechanical polishing (CMP) may optionally be performed.

Examples of materials of the planarizing layer include organic materialssuch as resins, and inorganic materials such as SiNx, SiOx, and Al₂O₃.The planarizing layer may be made of an organic compound or a mixturethereof. The planarizing layer can be formed by the same method as thatfor the protective layer.

Wavelength Selection Unit

The wavelength selection unit 8 is disposed on the planarizing layer. Inthe case where the planarizing layer is not provided, the wavelengthselection unit is disposed on the protective layer. In other words, thewavelength selection unit is disposed on the light incident side of thephotoelectric conversion element. Examples of the wavelength selectionunit include color filters, scintillators, and prisms.

Color filters transmit light having a predetermined wavelength more thanlight having other wavelengths. For example, by using three types offilters, that is, RGB filters, the entire visible light range can becovered. When the three RGB filters are used, the color filters may bearranged in the Bayer pattern, the delta pattern, or other patterns. Thewavelength selection unit may be a prism that separates only lighthaving a predetermined wavelength.

The position of the wavelength selection unit 8 is not limited to theposition shown in FIG. 3 . The wavelength selection unit is disposed atany position in a light path extending from a subject or a light sourceto the photoelectric conversion layer 1.

Lens

The microlens 9 is an optical member for collecting external light intothe photoelectric conversion layer. Although FIG. 3 illustrates ahemispheric lens, the microlens may have any other shape.

The microlens is made of, for example, quartz, silicone, or an organicresin. The shape and the material of the microlens are not limited aslong as the collection of light is not impaired.

Other Configurations

The photoelectric conversion element may include another photoelectricconversion element on the electrode. The use of the other photoelectricconversion element that photoelectrically converts light having adifferent wavelength enables light beams having different wavelengths tobe detected at the same or substantially the same in-plane position onthe substrate.

The photoelectric conversion element may further include another organiccompound layer that photoelectrically converts light having a wavelengthdifferent from the wavelength of light photoelectrically converted bythe organic compound layer. The organic compound layer and the otherorganic compound layer may be stacked on top of each other. Thisconfiguration, as with the configuration in which photoelectricconversion elements are stacked on top of each other, enables lightbeams having different wavelengths to be detected at the same positionor substantially the same position on the substrate.

Image Pickup Element According to Embodiment and Image Pickup ApparatusIincluding the Same Image Pickup Element

The photoelectric conversion element according to the present embodimentcan be used for an image pickup element. The image pickup elementincludes a plurality of photoelectric conversion elements serving aslight-receiving pixels, a readout circuit connected to the photoelectricconversion elements, and a signal processing circuit connected to thereadout circuit. Information based on charges that have been read out istransmitted to a signal processing unit connected to the image pickupelement. The signal processing unit may be, for example, a CMOS sensoror a CCD sensor. Information acquired by the light-receiving pixels isgathered and transmitted to the signal processing unit, whereby an imageis formed.

The image pickup element includes the plurality of photoelectricconversion elements, and the plurality of photoelectric conversionelements may include different color filters. The different colorfilters transmit light beams having different wavelengths. Specifically,the plurality of photoelectric conversion elements may include RGB colorfilters.

The plurality of photoelectric conversion elements may include thephotoelectric conversion layer as a common layer. The term “commonlayer” means that the photoelectric conversion layer of onephotoelectric conversion element and the photoelectric conversion layerof a photoelectric conversion element adjacent thereto are joinedtogether.

FIG. 4 is a circuit diagram of a pixel including the photoelectricconversion element according to the present embodiment. A photoelectricconversion element 10 is connected to a common line 19 at a node A 20.The common line may be connected to the ground.

A pixel 18 may include the photoelectric conversion element 10 and areadout circuit for reading a signal generated in a photoelectricconversion unit. The readout circuit may include, for example, atransfer transistor 11 electrically connected to the photoelectricconversion element, an amplifier transistor 13 including a gateelectrode electrically connected to the photoelectric conversion element10, a selection transistor 14 that selects a pixel from whichinformation is read out, and a reset transistor 12 that supplies a resetvoltage to the photoelectric conversion element.

The transfer by the transfer transistor 11 may be controlled with a gatevoltage. The supply of a reset voltage by the reset transistor may becontrolled with a voltage applied to the gate. The selected orunselected state of the selection transistor is determined by the gatevoltage.

The transfer transistor 11, the reset transistor 12, and the amplifiertransistor 13 are connected together at a node B 21. The transfertransistor may be omitted in some configurations.

The reset transistor 12 supplies a voltage to reset the potential at thenode B. The supply of the voltage can be controlled by applying a signalto the gate of the reset transistor. The reset transistor may be omittedin some configurations.

The amplifier transistor 13 generates a current depending on thepotential at the node B. The amplifier transistor is connected to theselection transistor 14 that selects a pixel from which a signal isoutput. The selection transistor 14 is connected to a current source 16and a column output unit 15. The column output unit 15 is connected to asignal processing unit.

The selection transistor 14 is connected to a vertical output signalline 17. The vertical output signal line 17 is connected to the currentsource 16 and the column output unit 15.

FIG. 5 schematically illustrates an image pickup element according to anembodiment. An image pickup element 28 includes an image pickup region25 and a peripheral region 26. The image pickup region 25 includes atwo-dimensional array of pixels. The region excluding the image pickupregion is the peripheral region. The peripheral region includes avertical scanning circuit 21, a readout circuit 22, a horizontalscanning circuit 23, and an output amplifier 24. The output amplifier isconnected to a signal processing unit 27. The signal processing unitperforms signal processing on the basis of information read by thereadout circuit. The signal processing unit may be, for example, a CCDcircuit or a CMOS circuit.

The readout circuit 22 includes, for example, a column amplifier, acorrelated double sampling (CDS) circuit, and an adding circuit. Thereadout circuit 22 performs amplification or addition of signals read,via a vertical signal line, from pixels in a row selected by thevertical scanning circuit 21. The column amplifier, the CDS circuit, theadding circuit, and so forth are disposed, for example, for each pixelcolumn or for every two or more pixel columns. The CDS circuit performsCDS signal processing and kTC noise reduction. The horizontal scanningcircuit 23 produces a signal for sequentially reading a signal from thereadout circuit 22. The output amplifier 24 amplifies a signal from acolumn selected by the horizontal scanning circuit 23 and outputs thesignal.

The above configuration is only an example of a photoelectric conversionapparatus, and the present embodiment is not limited to thisconfiguration. The readout circuit 22, the horizontal scanning circuit23, and the output amplifier 24 are each disposed above and below theimage pickup region 25 to constitute two output paths. The number ofoutput paths may be three or more. Signals from the output amplifiersare synthesized into an image signal in the signal processing unit.

Image Pickup Apparatus

The image pickup element according to the present embodiment can be usedfor an image pickup apparatus. The image pickup apparatus includes animage pickup optical system including a plurality of lenses and an imagepickup element that receives light that has passed through the imagepickup optical system. The image pickup apparatus includes the imagepickup element and a housing that houses the image pickup element. Thehousing may have a joint connectable to the image pickup optical system.More specifically, the image pickup apparatus is a digital camera or adigital still camera.

The image pickup apparatus may further include a communication unit thatallows a captured image to be viewed from the outside. The communicationunit may include a receiving unit that receives a signal from theoutside and a transmitting unit that transmits information to theoutside. Signals received by the receiving unit control at least one ofan image pickup range, a start of image pickup, and an end of imagepickup of the image pickup apparatus. The transmitting unit may transmitnot only captured images but also information such as warning aboutimages, remaining data capacity, and remaining power.

When including a receiving unit and a transmitting unit, the imagepickup apparatus can be used as a network camera.

EXAMPLES Example 1: Synthesis of Exemplary Compound A1

Exemplary compound A1 was synthesized according to the followingsynthesis scheme.

Synthesis of Compound D3

The following reagents and solvents were placed in a 300 mL recoveryflask.

-   Compound D1: 2.00 g (4.10 mmol)-   Compound D2: 1.83 g (10.3 mmol)-   Tetrakis(triphenylphosphine)palladium(0): 95 mg (0.08 mmol)-   Toluene: 40 ml-   Ethanol: 20 ml-   2M aqueous cesium carbonate solution: 40 ml

Next, the reaction solution was heated to reflux with stirring for 7hours in a nitrogen atmosphere. After completion of the reaction, thereaction product was extracted with chloroform. The organic layerobtained by the extraction was dried over sodium sulfate and thenconcentrated under reduced pressure to obtain a crude product. Next, thecrude product was purified by silica gel column chromatography (eluent:chloroform/heptane = ⅒) to obtain 1.55 g of compound D3 (yield: 75%).

Synthesis of Compound D5

The following reagents and solvents were placed in a 300 mL three-neckedflask.

-   Compound D3: 1.50 g (3.00 mmol)-   Compound D4: 2.49 g (15.9 mmol)-   Tetrakis(triphenylphosphine)palladium(0): 92 mg (0.08 mmol)-   Toluene: 40 ml-   Ethanol: 20 ml-   2 M aqueous cesium carbonate solution: 40 ml

Next, the reaction solution was heated to reflux with stirring for 7hours in a nitrogen atmosphere. After completion of the reaction, thereaction product was extracted with chloroform. The organic layerobtained by the extraction was dried over sodium sulfate and thenconcentrated under reduced pressure to obtain a crude product. Next, thecrude product was purified by silica gel column chromatography (eluent:chloroform/heptane = ⅒) to obtain 1.25 g of compound D4 (yield: 74%).

Synthesis of Compound A1

The following reagents and solvents were placed in a 300 mL three-neckedflask.

-   Compound D4: 1.20 g (2.13 mmol)-   Compound D5: 2.75 g (9.85 mmol)-   Tris(dibenzylideneacetone)dipalladium(0): 150 mg (0.16 mmol)-   Xphos: 234 mg (0.49 mmol)-   Dehydrated xylene: 90 ml-   Sodium t-butoxide: 945 mg (9.85 mmol)

Next, the reaction solution was heated to reflux with stirring for 7hours in a nitrogen atmosphere. After completion of the reaction, thereaction product was filtered through a membrane filter to obtain afiltrate. The filtrate obtained was washed with water, dried over sodiumsulfate, and then concentrated under reduced pressure to obtain a crudeproduct. Next, the crude product was purified by silica gel columnchromatography (eluent: toluene) and washed by heating dispersion withethanol to obtain 0.6 g of compound A1 (yield: 27%).

Exemplary compound A1 was identified by the following method.

-   Matrix-assisted laser desorption/ionization time-of-flight mass    spectrometry (MALDI-TOF-MS) (Autoflex LRF manufactured by Bruker)-   Measured value: m/z = 937.47, calculated value: C₇₀H₆₈N₂ = 937.30-   Measurement of thermophysical properties

The glass transition temperature of exemplary compound A1 was measuredby DSC to be 180° C.

Example 2: Synthesis of Exemplary Compound A2

Exemplary compound A2 was synthesized in the same manner as in Example 1except that compound D2 was replaced with compound D7 in the step (1).

The compound obtained was identified and measured for its thermophysicalproperties. The results are shown below.

-   MALDI-TOF-MS-   Measured value: m/z = 1049.84, calculated value: C₇₀H₆₈N₂ = 1049.51-   Measurement of glass transition temperature-   Glass transition temperature: 200° C.

Example 3: Synthesis of Exemplary Compound A15

Exemplary compound A15 was synthesized in the same manner as in Example1 except that compound D2 was replaced with compound 7 in the step (1)and that compound D4 was replaced with compound D8 in the step (2).

The compound obtained was identified and measured for its thermophysicalproperties. The results are shown below.

-   MALDI-TOF-MS-   Measured value: m/z = 1149.56, calculated value: C₈₆H₆₈NO₂ = 1149.63-   Measurement of glass transition temperature-   Glass transition temperature: 230° C.

Example 4: Synthesis of Exemplary Compound A9

Exemplary compound A9 was synthesized according to the followingsynthesis scheme.

Synthesis of Compound D10

The following reagents and solvents were placed in a 300 mL recoveryflask.

-   Compound D1: 2.00 g (4.10 mmol)-   Compound D9: 1.83 g (10.3 mmol)-   Tetrakis(triphenylphosphine)palladium(0): 95 mg (0.08 mmol)-   Toluene: 40 ml-   Ethanol: 20 ml-   2 M aqueous cesium carbonate solution: 40 ml

Next, the reaction solution was heated to reflux with stirring for 7hours in a nitrogen atmosphere. After completion of the reaction, thereaction product was extracted with chloroform. The organic layerobtained by the extraction was dried over sodium sulfate and thenconcentrated under reduced pressure to obtain a crude product. Next, thecrude product was purified by silica gel column chromatography (eluent:chloroform/heptane = ⅒) to obtain 1.55 g of compound D3 (yield: 75%).

Synthesis of Compound A9

The following reagents and solvents were placed in a 300 mL three-neckedflask.

-   Compound D10: 1.50 g (3.00 mmol)-   Compound D11: 2.49 g (15.9 mmol)-   Tetrakis(triphenylphosphine)palladium(0): 92 mg (0.08 mmol)-   Toluene: 40 ml-   Ethanol: 20 ml-   2 M aqueous cesium carbonate solution: 40 ml

Next, the reaction solution was heated to reflux with stirring for 7hours in a nitrogen atmosphere. After completion of the reaction, thereaction product was extracted with chloroform. The organic layerobtained by the extraction was dried over sodium sulfate and thenconcentrated under reduced pressure to obtain a crude product. Next, thecrude product was purified by silica gel column chromatography (eluent:chloroform/heptane = ⅒) to obtain 1.25 g of compound A9 (yield: 74%).

The compound obtained was identified and measured for its thermophysicalproperties. The results are shown below.

-   MALDI-TOF-MS-   Measured value: m/z = 937.26, calculated value: C₇₀H₆₈N₂ = 937.30-   Measurement of glass transition temperature-   Glass transition temperature: 190° C.

Example 5: Synthesis of Exemplary Compound A25

Exemplary compound A25 was synthesized in the same manner as in Example4 except that compound D9 was replaced with compound D12 in the step (1)and that compound D11 was replaced with compound D13 in the step (2).

The compound obtained was identified and measured for its thermophysicalproperties. The results are shown below.

-   MALDI-TOF-MS-   Measured value: m/z = 937.28, calculated value: C₇₈H₈₄N₂ = 1049.51-   Measurement of glass transition temperature-   Glass transition temperature: 190° C.

Example 6: Synthesis of Exemplary Compound B3

Exemplary compound B3 was synthesized in the same manner as in Example 1except that compound D2 was replaced with compound D7 in the step (1)and that compound D4 was replaced with compound D14 in the step (2).

The compound obtained was identified and measured for its thermophysicalproperties. The results are shown below.

-   MALDI-TOF-MS-   Measured value: m/z = 1049.73, calculated value: C₇₈H₈₄N₂ = 1049.51-   Measurement of glass transition temperature-   Glass transition temperature: 190° C.

Example 7: Synthesis of Exemplary Compound C6

Exemplary compound C6 was synthesized in the same manner as in Example 1except that compound D2 was replaced with compound D15 in the step (1).

The compound obtained was identified and measured for its thermophysicalproperties. The results are shown below.

-   MALDI-TOF-MS-   Measured value: m/z = 1049.51, calculated value: C₇₄H₆₈N₂S₂ =    1049.48-   Measurement of glass transition temperature-   Glass transition temperature: 190° C.

Example 8: Synthesis of Exemplary Compound C17

Exemplary compound C17 was synthesized in the same manner as in Example1 except that compound D2 was replaced with compound D16 in the step(1).

The compound obtained was identified and measured for its thermophysicalproperties. The results are shown below.

-   MALDI-TOF-MS-   Measured value: m/z = 939.21, calculated value: C₆₈H₆₆N₄ = 939.28-   Measurement of glass transition temperature-   Glass transition temperature: 190° C.

Comparative Example 1: Synthesis of Comparative Compound 2

Comparative compound 2 was synthesized in the same manner as in Example1 except that compound D6 was replaced with compound D17 in the step(3).

The compound obtained was identified and measured for its thermophysicalproperties. The results are shown below.

-   MALDI-TOF-MS-   Measured value: m/z = 712.41, calculated value: C₅₄H₆₆N₂ = 712.88-   Measurement of glass transition temperature-   Glass transition temperature: 160° C.

Comparative Example 2: Synthesis of Comparative Compound 3

Comparative compound 3 was synthesized in the same manner as in Example1 except that compound D2 was replaced with compound D7 in the step (1)and that compound D6 was replaced with compound D18 in the step (3).

The compound obtained was identified. The results are shown below.

-   MALDI-TOF-MS-   Measured value: m/z = 1017.56, calculated value: C₇₈H₅₂N₂ = 1017.26

Sublimation purification of comparative compound 3 was resulted infailure, and thus an element containing comparative compound 3 could notbe fabricated.

Example 9: Fabrication of Photoelectric Conversion Element

An organic photoelectric conversion element was fabricated in a mannerdescribed below. In the organic photoelectric conversion element, acathode, an electron blocking layer (a first organic compound layer), aphotoelectric conversion layer (a second organic compound layer), a holeblocking layer (a third organic compound layer), and an anode weresequentially formed on a substrate.

First, an indium zinc oxide film was formed on a Si substrate and thenpatterned into a desired shape, thereby forming a cathode. The thicknessof the cathode was set to 100 nm. The substrate having the cathodeformed thereon was used as a substrate provided with an electrode in thefollowing process.

Next, organic compound layers and an electrode shown in Table 2 belowwere successively formed on the substrate provided with an electrode.The photoelectric conversion layer was formed by co-deposition, and itsmixing ratio and thickness are as shown in the table. At this time, theelectrode area of the counter electrode (anode) was set to 3 mm².Thereafter, a sealing layer was formed using SiN.

TABLE 2 Constituent material Thickness (nm) Electron blocking layerExemplary compound A2 100 Photoelectric conversion layer CG6:CG25 =50:50 (weight ratio) 400 Hole blocking layer Fullerene C60 50 Electroncollecting electrode Indium zinc oxide 30

Examples 10 to 19 and Comparative Examples 3 to 5: Fabrication ofPhotoelectric Conversion Element

Organic photoelectric conversion elements were fabricated in the samemanner as in Example 1 except that the electron blocking layer, thephotoelectric conversion layer, and the hole blocking layer wereappropriately changed as shown in Table 3 below. In Comparative Example3, comparative compound 3, which was unpurified by sublimation, was usedto deposit an electron blocking layer, but the rate of deposition wasunstable.

TABLE 3 Electron blocking layer Photoelectric conversion layer Holeblocking layer Example 10 Exemplary compound A2 CG5:CG25 = 50:50 (weightratio) Fullerene C60 Example 11 Exemplary compound A4 CG1 :CG25:Exemplary compound A2 = 40:40:20 (weight ratio) HBM1 Example 12Exemplary compound A6 CG2:Fullerene C60 = 20:80 (weight ratio) HBM1Example 13 Exemplary compound A1 CG2:Fullerene C60 = 30:70 (weightratio) HBM2 Example 14 Exemplary compound A12 CG18:CG21 = 50:50 (weightratio) HBM4 Example 15 Exemplary compound B1 CG9:Fullerene C60 = 50:50(weight ratio) [60]PCBM Example 16 Exemplary compound B5 CG10:FullereneC60 = 20:80 (weight ratio) Fullerene C60 Example 17 Exemplary compoundC6 CG28:Fullerene C60 = 30:70 (weight ratio) Exemplary compoundA2:Fullerene C60 = 30:70 (weight ratio) Example 18 Exemplary compound A2CG30:Fullerene C60 = 50:50 (weight ratio) Exemplary compoundA2:Fullerene C60 = 30:70 (weight ratio) Example 19 Exemplary compoundA21 CG10:CG27 = 50:50 (weight ratio) Exemplary compound A21:FullereneC60 = 30:70 (weight ratio) Com parative Example 3 Com parative compound2 CG6:CG25 = 50:50 (weight ratio) Fullerene C60 Com parative Example 4none CG1:CG25 = 50:50 (weight ratio) Comparative compound 2:FullereneC60 = 30:70 (weight ratio) Com parative Example 5 Com parative compound3 CG6:CG25 = 50:50 (weight ratio) Fullerene C60

Evaluation of Properties of Photoelectric Conversion Elements

The photoelectric conversion elements obtained in Examples andComparative Examples were measured and evaluated for their properties.

Current Properties

Specifically, a voltage of 5 V was applied to each element, and thecurrent flowing through the element at this time was measured. For eachof the organic photoelectric conversion elements fabricated in Examples,the ratio of a current in a bright place to a current in a dark place(current in bright place)/(current in dark place) was 100 or more. Thisindicates that the organic photoelectric conversion elements fabricatedin Examples function well.

Evaluations of Quantum Yield (External Quantum Yield) and Dark Current

The organic photoelectric conversion elements obtained were evaluatedfor changes in dark current and external quantum efficiency before andafter annealing. The effect of annealing in reducing dark current wasevaluated according to the following criteria: when the dark currentafter annealing was less than 0.5 relative to the dark current beforeannealing taken as 1, the element was graded as A; when it was 0.5 ormore and less than 1, the element was graded as B; and when it was 1.0or more, the element was graded as C.

The stability of element properties after annealing was evaluatedaccording to the following criteria: when the external quantumefficiency after annealing was 1.0 or more relative to the externalquantum efficiency before annealing taken as 1, the element was gradedas A; when it was 0.8 or more and less than 1.0, the element was gradedas B; and when it was less than 0.8, the element was graded as C. Theannealing was performed by allowing the element to sit on a hot plate at170° C. for 30 minutes in the ambient atmosphere.

The dark current was determined as the density of current flowing whenthe photoelectric conversion element was allowed to sit in a dark placewith a voltage of 5 V being applied between the cathode and the anode.

The external quantum efficiency was determined by measuring the densityof photocurrent flowing when the photoelectric conversion element wasirradiated with monochromatic light with an intensity of 50 µW/cm² at amaximum absorption wavelength of the element, with a voltage of 5 Vbeing applied between the cathode and the anode of the element.

The photocurrent density was determined by subtracting the dark currentdensity in the dark from the current density at the time of lightirradiation. The monochromatic light used for the measurement wasobtained by monochromatizing white light emitted from a xenon lamp(Model XB-50101AA-A, manufactured by Ushio, Inc.) with a monochromator(Model MC-10N, manufactured by Ritu Oyo Kougaku Co., Ltd.). Theapplication of voltage to the elements and the measurement of currentwere performed with a source meter (Model R6243, manufactured byAdvantest Corporation). The measurement of the external quantumefficiency was performed from the upper electrode side with light beingperpendicularly incident on the element. The results are shown in Table4.

TABLE 4 Dark current External quantum efficiency Example 9 A A Example10 A B Example 11 A A Example 12 B B Example 13 B B Example 14 A AExample 15 A B Example 16 A A Example 17 B B Example 18 A A Example 19 BB Comparative Example 3 C B Comparative Example 4 C C ComparativeExample 5 C B

Table 4 shows that the organic photoelectric conversion elementsaccording to the present invention exhibited significant reductions indark current after annealing and, in addition, maintained their externalquantum efficiency. In particular, when the number of tert-butyl groupswas 6 or more, the dark current was greatly reduced after annealing, andgood element properties were exhibited. This is probably because anamorphous thin film having high thermal stability was formed. Bycontrast, the organic photoelectric conversion elements of ComparativeExamples exhibited increases in dark current after annealing. This canbe explained as follows: when the material forming the electron blockinglayer had a low glass transition temperature, crystallization due toannealing resulted in degraded film quality, and when the deposited filmhad low purity, an impurity level was formed, thus resulting indegradation of element properties.

As described in EXAMPLES above, it was found that the presence of theorganic compound according to the present invention in an electronblocking layer can provide an organic photoelectric conversion elementwith reduced dark current and improved thermal stability.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1. An organic device comprising: an anode; a cathode; and an organiccompound layer being disposed between the anode and the cathode, whereinthe organic compound layer has a layer containing an organic compoundrepresented by general formula [1]:

wherein Ar₁ and Ar₂ may be the same or different and represent anaromatic hydrocarbon group having 6 to 18 carbon atoms or aheteroaromatic group having 3 to 17 carbon atoms, Ar₃ and Ar₄ may be thesame or different and are selected from the group consisting ofsubstituents represented by general formulae [2a] to [2c], in which *indicates a bonding position to a phenyl group represented by thegeneral formula [1]:

Ar₁ to Ar₄ are each optionally substituted with a substituent selectedfrom the group consisting of a halogen atom, a cyano group, an alkylgroup having 1 to 8 carbon atoms, and an alkoxy group having 1 to 8carbon atoms, the alkyl group being optionally substituted with afluorine atom, provided that at least one of Ar₁ to Ar₄ has a tert-butylgroup, and a total number of tert-butyl groups in one molecule of theorganic compound is 2 or more.
 2. The organic device according to claim1, wherein Ar₁ and Ar₂ are each a phenyl group, a naphthyl group, apyridyl group, a benzothienyl group, or a benzofuranyl group.
 3. Theorganic device according to claim 1, wherein Ar₃ and Ar₄ are each thesubstituent represented by formula [2a].
 4. The organic device accordingto claim 1, wherein the total number of tert-butyl groups in onemolecule of the organic compound is 4 or more.
 5. The organic deviceaccording to claim 1, wherein the total number of tert-butyl groups inone molecule of the organic compound is 6 or more.
 6. The organic deviceaccording to claim 1, wherein the organic compound layer includes afirst organic compound layer and a second organic compound layer, thesecond organic compound layer being disposed between the first organiccompound layer and the cathode, and wherein the layer containing theorganic compound represented by general formula [1] is the secondorganic compound layer.
 7. The organic device according to claim 6,wherein the second organic compound layer is in contact with thecathode.
 8. The organic device according to claim 6, wherein the firstorganic compound layer is a photoelectric conversion layer, and thephotoelectric conversion layer contains a fullerene and a fullereneanalogue.
 9. The organic device according to claim 6, wherein theorganic compound layer includes a third organic compound layer, thethird organic compound layer being disposed between the first organiccompound layer and the anode, and the third organic compound layercontains a fullerene and a fullerene analogue.
 10. The organic deviceaccording to claim 9, wherein the third organic compound layer is incontact with the anode.
 11. An image pickup element comprising: aplurality of photoelectric conversion elements; a readout circuitconnected to the photoelectric conversion elements; and a signalprocessing circuit connected to the readout circuit, wherein thephotoelectric conversion elements are each the organic device accordingto claim
 1. 12. An image pickup apparatus comprising: an optical systemincluding a lens; and an image pickup element that receives light thathas passed through the optical system, wherein the image pickup elementis the image pickup element according to claim
 11. 13. An image pickupapparatus comprising: a housing provided with a joint connectable to anoptical system including a plurality of lenses; and an image pickupelement housed in the housing, wherein the image pickup element is theimage pickup element according to claim
 11. 14. The image pickupapparatus according to claim 12, wherein the image pickup apparatus is adigital camera or a digital still camera.
 15. The image pickup apparatusaccording to claim 12, further comprising a communication unit thattransmits or receives information to or from an outside.